Explain the working of npn and pnp transistor - M R Academic Care

Working of npn transistor shows the npn transistor with forward bias to emitter base junction and reverse bias to collector base junction. 

The forward bias causes the electrons in the n-type emitter to flow towards the base. This constitutes the emitter current IE. As these electrons flow through the p-type base, they tend to combine with through the p-type base, the tend to combine with holes. 

As the base is lightly doped and very thin. Therefore, only a few electrons (less than 57%) combine with holes to constitute base current IB. The remainder (more than 95%) cross over into the collector region to constitute collector current IC. 

In this way, almost the entire emitter current flows in the collector circuit. It is clear that emitter current is the sum of collector and base currents i.e.

Working of pnp transistor: The basic connection of a pnp transistor. The forward bias causes the holes in the p-type emitter to flow towards the base. This constitute the emitter current IE. 

As these holes cross into n-type base, they tend to combine with the electrons. As the base is lightly doped and very thin. 

Therefore, only a few holes (less than 5%) combine with the electrons. The remainder (more than 95%) cross into the collector region to constitute collector current IC. In this way, almost the entire emitter current flows in the collector circuit. In it may be noted that current conduction within pnp connecting wires, the current is still by electrons.